EP0262040A1 - Process for treating a paper pulp with an enzymatic solution - Google Patents

Abstract

According to the process, an enzyme preparation containing cellulases and/or hemicellulases is reacted with a homogeneous aqueous suspension of the papermaking pulp exhibiting a Schopper-Riegler (SR) value determined in accordance with NFQ standard 50 003 of at least 25. <??>Application of the process for the treatment of a papermaking pulp based on recycled fibres.

Description

The present invention relates to the paper industry and in particular the recycled paper industry and more specifically it relates to a new process for treating paper pulp using an enzymatic solution.

The paper industry is using more and more recycled paper. For example, to manufacture corrugated cardboard, more and more raw materials based on recycled fibers are used, and the number of recycles is increased in parallel. With each recycling, the quality of the raw materials is further degraded. To find a satisfactory level of mechanical characteristics, a refining of the doughs in aqueous suspension is generally carried out, which causes machinability difficulties.

The pulp in aqueous suspension ready to be used on a paper machine can be characterized by various parameters, one of which is particularly significant for predicting the suitability of the pulp for draining. The Schopper-Riegler degree (SR) of a pulp is thus defined as being an element of appreciation of the quality of a pulp for papermaking. It expresses the ability of water to separate from the suspension under the conditions defined by standard NFQ 50 003. On a scale ranging from 0 to 100, a high value of SR indicates a low speed of drainage of the suspension while a low value indicates a faster drip speed. It has been observed, for example, that a dough which has undergone a refining operation has its SR more or less increased according to the degree of refining undergone, compared to a dough which has undergone little or no such operation.

This parameter plays a particularly important role in the performance of the paper machine. Indeed, to increase the yield, the draining phase must take the least time possible. For suspensions with a high SR, it is necessary to increase the concentration of the pasta to maintain the same production rate. This results in poorer leaf formation because the fibers are more difficult to distribute. It is therefore particularly advantageous to have suspensions with a fairly low SR.

It is believed that as soon as suspensions have an SR greater than 25, it becomes desirable to try to lower it to improve the conditions for papermaking. Such a reduction is desirable according to two aspects: on the one hand, the yield on the paper machine can be improved thanks to the acceleration of the drainage; on the other hand, the production rates can be kept without having to compensate for the slowness of the drainage by a lesser dilution of the suspension, with the risks that this would entail poor formation of the sheets.

The invention aims to provide a method for treating pulp in aqueous suspension, such as suspensions based on recycled fibers, having an SR at least equal to 25 which, by the intervention of enzymes, makes it possible to lower the SR and therefore improve the drainage of the suspension and the yield of the paper forming process.

There are a number of processes known in the paper industry using enzyme preparations.

We know for example from the French patent publication FR 2 557 894 a process for treating paper pulp with an enzymatic solution which promotes the refining of the pulp, that is to say which makes it suitable for being transformed into paper. having defined characteristics. According to this process, a specific enzymatic solution containing xylanases is made to act on an unrefined paste and therefore having a fairly low SR of the order of 10.

This process therefore aims not to improve the drainage of the treated dough, but to improve its ability to refine.

Also known, from Canadian patent CA 758 488, is a process for refining a paper pulp which consists in subjecting an unrefined pulp to the action of an enzymatic solution based in particular on cellulase, pectinol or lipase, and on the simultaneously subject to mechanical refining. The aim is also to improve the refining of the treated pulp.

We also know, by the French patent publication FR 2 571 738 a process for treating a paper pulp according to which, in order to give the pulp the characteristics of a pulp for chemical use, an enzymatic preparation containing fungal cellulases having a C₁ activity is acted on the pulp and a C _x activity.

The method according to the invention applies not to unrefined pulp pulps, but to pulps which already have a high SR. The high value of the SR may result either from a prior mechanical refining which has made the pulp capable of providing a paper having good mechanical characteristics, or from the fact that the pulp has already undergone several recycling operations, or possibly from the combination of the two operations.

According to the invention, an enzyme preparation containing cellulases is made to act on a paper pulp having an SR at least equal to 25, measured on a pulp in homogeneous suspension at 2 g / l under the conditions of standard NF Q 50 003. and / or hemicellulases.

It is found that this treatment makes it possible to lower the SR of the pulp treated while having no undesirable effect on the mechanical characteristics of the papers produced from this pulp.

The treated paper pulps can be used for the most varied applications in the paper industry. These are pulps made from recycled fibers or unbleached or bleached chemical pulps for obtaining kraft paper. Mention may also be made of mechanical pulps, as they are used for the production of newsprint.

Among all the enzymatic preparations containing cellulases and / or hemicellulases, preference is given to those which have a C₁ activity, a C _x activity and a xylanasic activity. Without knowing exactly the role played by each of these activities, it would seem that the conjunction of the three leads to the desired effect. These three activities are defined by the international nomenclature of enzymes and they can be qualified and expressed in units of the international system per milligram of powder of the enzyme preparation considered. The activity Cactivité is the action of cellobiohydrolase which can be assayed on very organized pure cellulose. This activity is manifested by the production of cellobiose and the international system has retained the AVICEL substrate as the reference substrate. The activity C _x is measured on modified cellulose, carboxymethylcellulose and it is quantified by a fall of the screw cosity of carboxymethylcellulose or an increase in reducing activities. The xylanasic activity allows hydrolysis of the binding xylans.

Advantageously, the treatment with the enzymatic preparation is not continued beyond approximately 60 minutes, because the SR tends to rise slightly beyond this duration, while remaining significantly lower than the starting SR.

The enzyme preparation is used at an enzyme concentration which varies according to the C₁, C _x or xylanasic activities of the enzymes contained in the preparation. Thus, the enzymatic preparation is preferably at a concentration of 0.01% to 2% of the weight of the dry dough, these percentages corresponding to a preparation having a C₁ activity of 0.168 USI per milligram of powder, an activity C _x of 3.9 USI per milligram of powder and a xylanasic activity of 31 USI per milligram of powder.

It goes without saying that the concentrations of enzymatic preparations must be adapted according to the type of preparation used. The fact remains that generally, below a concentration equal to about 0.01% of the weight of the dry dough, no significant effect is observed, except to extend the reaction time. Beyond a concentration equal to about 2% of the weight of the dry pulp, the cost of the operation tends to become prohibitive, and the mechanical characteristics of the paper produced tend to decrease.

The reaction medium can be more or less suitable for the action of enzymes. Temperature and pH conditions are more particularly suitable for avoiding any risk of denaturation of the enzymes by the medium. The pH is thus advantageously between 3 and 7, and the temperature between 20 ° C and 60 ° C. Above 60 ° C, the medium tends to denature the enzyme, and below 20 ° C, the action of the enzymes manifests itself particularly slowly.

A good example of application of the method according to the invention is represented by the suspended pulps based on recycled fibers. The treatment according to the invention makes it possible to significantly improve the yield on the paper machine. According to a particularly advantageous embodiment of the invention, the enzymatic treatment is preceded in this application by a conventional mechanical refining. It has been found that the mechanical properties of the paper produced are also improved under these conditions, and in particular the burst index or the CMT.

For all pulps which lead to the formation of papers whose mechanical characteristics are deemed insufficient, a starch coating is advantageously carried out after the sheets have been formed and dried on the paper machine. Under these conditions, not only does one obtain a lowering of the SR, thanks to the enzymatic treatment but also an increase of the mechanical characteristics such as the burst index or the CMT, thanks to the coating of starch.

After the enzymatic treatment, the pulp in suspension is implemented on a usual paper machine which comprises a manufacturing table provided with a box providing a jet of pulp in aqueous suspension for the formation of a sheet of paper with a layer , the manufacturing table being covered with a fabric for draining the dough, a press section, a drying section and possibly a size press for coating starch.

Other characteristics and advantages of the invention will appear during the following detailed description of exemplary embodiments.

In all the examples reported, the characteristics indicated are defined as follows:
- Schopper-Rieger degree (SR): in accordance with standard NFQ 50 003 (measured on a paste in homogeneous suspension at 2 g / l)
- burst index: in accordance with standard NFQ 03 053, it is quantified by the quotient of the maximum pressure distributed uniformly, and supported by a test piece of paper, perpendicular to its surface, by the grammage of the paper,
- CMT (Corrugated medium test): the value indicated reflects the flat compression resistance of a corrugated paper and constitutes an edge compression index. The test is carried out as follows: the paper is compressed after being conditioned for 60 minutes.

EXAMPLE 1

An aqueous suspension of paper pulp based on recycled fibers is prepared in the following way: 5 kg dry weight of a pulp consisting of 40% of fibers from recycled cardboard boxes (CCR) and 60% of fibers from is weighed from the warehouse and put it in a reactor. It is made into an aqueous suspension at 3.5% in weight by adding water up to a total weight of 143 kg. The pH of the suspension is adjusted to 4.8 by adding 900 cc of 1N H₂SO₄. The reactor is stirred at a speed of 50 revolutions / minute to homogenize the suspension. The reactor is preheated for 90 minutes until reaching 50 ° C., then 0.1% by weight is introduced relative to the weight of dry paste of enzymes prepared in the following manner: 5 g of a Maxazyme powder are taken CL 2000, marketed by the company RAPIDASE. The product sold under this designation is characterized by the fact that it comes from the culture of the microorganism Trichoderma viridae , that it has a C₁ activity of 0.168 USI, a C _x activity of 3.91 USI, a xylanasic activity of 31 USI and an FPU (Filter paper unit) of 0.28. This powder is placed in 2800 g of water brought to a pH of 4.8 and the aqueous enzyme solution thus prepared is introduced into the reactor. The maxazyme is allowed to react for 30 minutes.

The reaction is stopped by diluting the contents of the reactor until a suspension of 7 g per liter is obtained.

The SR is measured in the context of the example just before the introduction of the enzymes and 30 minutes after the introduction of the enzymes. Its value goes from 54 to 44.

A control suspension which is not treated with the enzymatic solution is simultaneously prepared, under identical conditions, and the suspensions are sent to a pilot paper machine to form a single-layer sheet with a basis weight of 120 g / m².

The following mechanical characteristics are noted:

It is observed that the treatment has not deteriorated the mechanical characteristics.

EXAMPLE 2

The conditions of Example 1 are repeated, except that before the introduction of the enzymes, the suspension paste is mechanically refined using a SPROUT-WALDRON refiner until an SR of 74 is obtained. 30 minutes after the introduction of enzymes, the SR is lowered to 59.

The following mechanical characteristics are noted:

There is therefore a clear improvement in mechanical characteristics, while the negative effects of mechanical refining on the value of SR are offset. For a final SR (59) roughly identical to the initial SR (54), the mechanical characteristics of the paper produced have been increased.

EXAMPLE 3

The conditions of Example 1 are repeated, except that after having formed the sheet of paper, it is coated with starch, at a rate of 5 g / m², using a size press.

The control was coated with starch but not treated with enzymes.

The following mechanical characteristics are noted:

There is a conservation of mechanical characteristics at a high level. In comparison with the control of Example 1, the treatment carried out under the conditions of Example 3 therefore not only made it possible to lower the SR, but also to increase the mechanical characteristics.

EXAMPLE 4

The conditions of example 2 are repeated, subjecting the paper to the starch treatment described in example 3.

The following mechanical characteristics are noted.

The witness was coated with starch, but neither treated with enzymes, nor mechanically refined.

An even clearer improvement in mechanical characteristics is observed than that observed in Example 3.

EXAMPLE 5

The conditions of Example 1 are repeated, except that the maxazyme CL 2000 is replaced by the 250 P cellulase marketed by the company GENENCOR. This liquid enzyme preparation is characterized by the following activities:
C₁ (AVICEL) 0.008 ICU / mg powder
C _x (CMC) 0.12 USI / mg powder
xylanasic 0.11 USI / mg powder
FPU 0.26 USI / mg powder

The starting pulp is also modified. This time, it is made up of 75% CCR and 25% warehouse fat and makes an aqueous suspension of 3%.

The SR goes from 39.5 to 29.5.

The following mechanical characteristics are noted:

EXAMPLE 6

The conditions of Example 5 are repeated, replacing the 250 P cellulase by the enzyme preparation SP 249 derived from the microorganism Aspergillus niger and sold by the company NOVO.

This enzymatic preparation, liquid, is characterized by the following activities:
C₁ (AVICEL) 8 USI / ml solution
C _x (CMC) 108 ICU / mg solution
xylanasic 560 ICU / mg solution
FPU 1 ICU / mg solution

This preparation is introduced at a concentration of 2.65% of the weight of the dough dry.

The SR goes from 34.5 to 27.

The following mechanical characteristics are noted:

It can be seen that the mechanical characteristics are maintained.

EXAMPLE 7

Under the same conditions as in Example 1, a 5% aqueous suspension of a paper pulp composed of 100% bulk from a warehouse is prepared. 0.25% by weight of dry paste is introduced this time of the enzymatic preparation of Example 1.

The SR goes from 48 to 35.5.

Adequate mechanical characteristics are observed.

EXAMPLE 8

A kraft chemical pulp of bleached short fibers is prepared and a 5% suspension is made. The procedure is that described in Example 1, except that the enzymatic preparation is introduced at a concentration of 0.25% by weight of dry paste and the enzymes are made to act for 60 minutes.

Before the enzymatic treatment, the dough is refined mechanically, so as to increase the SR from 18 to 25. After the enzymatic treatment, it is found that the SR has been lowered to 20.

For chemical pulps, other mechanical characteristics are significant than those used for pulps made from recycled fibers, due to the different qualities that are demanded of paper.

The burst index will always be retained, but also the length of rupture by traction.

The tensile strength is determined according to the conditions defined in standard NFQ 03 004. This is the calculated length limit, beyond which a strip of paper of any width, but uniform, assumed to be suspended by one of its ends, breaks under the effect of its own weight.

The following mechanical characteristics are noted:

Compared to the witness, it can be seen that the mechanical characteristics have been maintained.

EXAMPLE 9

The same conditions are repeated as in Example 8, except that the dough is mechanically refined before obtaining an SR of 31. After the enzymatic treatment, the SR is lowered to 22.

The following mechanical characteristics are noted:

It is noted, compared with Example 8, that when starting from a higher initial SR, corresponding to a more refined pulp, the implementation of which leads to the production of paper s having better mechanical characteristics, Thanks to the invention, it is easier to lower the SR, without deteriorating the mechanical characteristics. Thus, not only do we have satisfactory mechanical characteristics, but also a good yield on the paper machine. In Example 8, the SR is lowered from 25 to 20 after the enzyme treatment, a drop of 20%. In Example 9, the SR is lowered from 31 to 22 after an identical enzymatic treatment, ie a fall of 29%.

EXAMPLE 10

We prepare a chemical kraft pulp of long white fibers chies which are suspended at 5%. The conditions are identical to those of Example 8, except that the pH of the medium is adjusted to 6 and the temperature is brought to 20 ° C.

The initial SR is 12, the dough undergoes mechanical refining prior to the enzymatic treatment which brings the SR to 25. After the enzymatic treatment, it is lowered to 21.

It can therefore be seen that by modifying the temperature and pH conditions, the action of the enzymes is not inhibited.

The following mechanical characteristics are noted:

It is noted that, compared to the control that is mechanically refined, but not treated with enzymes, the level of mechanical characteristics is preserved. The higher values of the break length of the control and of the example are due to the fact that the dough comprises long fibers and no longer short fibers.

Claims (11)

1. Process for treating a paper pulp by an enzymatic preparation, characterized in that one acts on a homogeneous aqueous suspension of said paper pulp, having a Schopper-Riegler degree (SR) determined in accordance with standard NFQ 50 003, at least 25, an enzyme preparation containing cellulases and / or hemicellulases. 2. Method according to claim 1, characterized in that an enzymatic preparation containing enzymes derived from the microorganism Trichoderma viridae is used . 3. Method according to claim 1, characterized in that an enzymatic preparation is used containing enzymes derived from the microorganism Aspergillus niger . 4. Method according to one of claims 1 to 3, characterized in that the action of the enzymatic preparation is continued for a duration less than or equal to 60 minutes. 5. Method according to one of the preceding claims, characterized in that the reaction medium has a pH between 3 and 7. 6. Method according to one of the preceding claims, characterized in that the reaction medium is brought to a temperature between 20 ° C and 60 ° C, preferably around 50 ° C. 7. Method according to one of the preceding claims, characterized in that the enzymatic preparation is introduced at a concentration of 0.01% to 2% by weight relative to the total weight of dry paper pulp, the percentages indicated corresponding to an enzymatic preparation powder having a C₁ activity (AVICEL) of 0.168 USI / mg of powder, a C _x activity (CMC) of 3.91 USI / mg of powder and a xylanasic activity of 31 USI / mg of powder. 8. Method according to claim 7, characterized in that the concentration of the enzymatic preparation is 0.1% by weight relative to the total weight of dry pulp. 9. Method according to one of claims 1 to 8 characterized in that it applies to the treatment of a paper pulp composed of recycled fibers. 10. Method according to claim 8, characterized in that after the treatment with the enzymatic preparation, the pulp is used on a paper machine, and the paper formed is coated with starch. 11. Method according to one of claims 1 to 10, characterized & <DPA N = 2> in that the dough is previously refined mechanically, before treatment with the enzyme preparation.